Damping foil consisting of several layers and a method for producing same

ABSTRACT

The present invention provides a multi-layer damping foil ( 2 ) the lower layer ( 3 ) of which, facing towards the part (sheet  1 ) to be damped, has properties which are suitable for the adhering of the damping foil ( 2 ) onto the part ( 1 ), and the upper layer ( 4 ) thereof, facing away from the part ( 1 ), does not have the adherence properties, For weight reduction, the lower layer ( 3 ) has numerous through openings ( 7 ). Advantageously there is provided between the two layers ( 3, 4 ) a thin film-like intermediate layer ( 5 ) of non-woven fabric, kraft paper or the like, which may likewise have openings ( 8 ). The properties bringing about the adherence can be formed by means of an appropriate constituting of the material of the lower layer ( 3 ) and/or the mixing in of magnetic or magnetisable particles (parts  10 ). The layers ( 3, 4, 5 ) can be laminated onto one another. The upper layer ( 4 ) can also be so constituted that upon application of the corresponding material it brings about penetrations  9  into the openings  7  of the upper separation layer ( 3 ).

[0001] The invention relates to a multi-layer damping foil oranti-drumming foil having the features of the preamble of claim 1.

[0002] Damping foils or anti-drumming foils are employed, in particularin the automobile industry, for the sound deadening, i.e. sound damping,of sheets or panels. In particular, such damping foils can be placed inthe interior roof and side regions of a body and there adhere firmly allover the surface. Frequently, such damping foils are painted over. Theall-over surface adherence is attained, in accordance with the state ofthe art, in that the side of the damping foil towards the sheet or panelto be damped is provided with a hot-melt glue and after application ofthe damping foil onto the sheet to be damped a heat treatment is carriedout which brings about the melting of the hot-melt glue and therewithattains the all-over surface gluing. In order to be able to hold thedamping foil in position before the heat treatment, in particular in thecase of roof and side regions of a body, in accordance with the state ofthe art such a damping foil is constituted to be magnetisable. For thispurpose, previously, rod or strip-shaped metal parts have been set intothe side of the damping foil towards the sheet to be damped (DE 38 25494 A1) or there are mixed into the damping foil, in its production,ferrite powder or similar magnetic or magnetisable powdery particles (DE34 27 916 A1). Damping foils constituted in this way adhere during theheat treatment to the body sheeting due to their own magneticproperties, or due to permanent magnets arranged on the outer side ofthe sheeting, which attract the magnetisable particles in the dampingfoil and therewith the entire damping foil. After it had been determinedthat it was sufficient to correspondingly constitute only a certainlayer thickness, it was proposed to employ a multi-layer structure withwhich a lower layer, towards the sheet or panel, contains magnetic ormagnetisable particles and that a layer away from the sheet or panel,which layer fulfils in substance the damping function, does not needsuch particles. Between these layers, both in general includingbituminous material, there can be embedded, in accordance with the stateof the art, a flexible foil of aluminium or polyethylene (EP 0 285 740B1).

[0003] In particular the layer towards the sheet to be damped, havingthe magnetic or magnetisable particles, has high mass per unit area andthus determines the overall weight of the damping foil to be applied toa very significant degree, without this layer contributing significantlyto the damping.

[0004] Starting from here, it is the object of the invention to improvea damping foil as explained above to the effect that without adverselyeffecting the sound damping behaviour and the readiness of applicationto the part to be damped, the mass per unit area is reduced.

[0005] This object is achieved in accordance with the invention in thatthe lower layer, towards the part to be damped, such as a body sheet,has numerous through-openings in the sense of being perforated.

[0006] The invention is further developed by the features of thesubclaims.

[0007] Of particular advantage, with regard to acoustic properties, isto provide between the two layers an intermediate layer of non-wovenfabric or kraft paper.

[0008] With a particular configuration for certain productiontechnologies it is expedient to provide these openings not only in thelower layer but also in the associated intermediate layer, such that thematerial of the upper layer upon its application can penetrate throughthe openings. Even if the mass per unit area of the lower layer isthereby slightly increased in comparison with a configuration in whichthe openings are filled with air, the damping foil can however beproduced overall more economically, since the material of the upperlayer can be applied to the lower layer, provided with the intermediatelayer, in a simple manner and bonds very well with lower layer andintermediate layer.

[0009] Alternatively, the lower layer can be formed also as adhesivelayer which whilst achieving an adherent connection is removable intact,as is per se known from DE 35 10 932 A1 or EP 0 195 923 B1.

[0010] In the production of a damping foil in accordance with theinvention, on a web or sheet material forming the lower layer, afterperforation thereof, a web or sheet material forming the upper layer islaminated on or applied in some other manner. If an intermediate layeris provided this is to be laminated onto the lower layer before or afterthe perforation of that layer. For example, the non-woven fabric or thekraft paper which forms intermediate layer may be constituted to beadhesive on both sides.

[0011] The invention will now be described in more detail with referenceto the exemplary embodiments illustrated in the drawings. There isshown:

[0012]FIG. 1 in an exploded and perspective illustration, a section of adamping foil in accordance with the invention viewed towards the sidefacing the part to be damped,

[0013]FIG. 2 in section, a damping foil, laid on a sheet to be damped,in accordance with a first exemplary embodiment,

[0014]FIG. 3 in section, a damping foil, laid on a sheet to be damped,in accordance with a second exemplary embodiment,

[0015]FIG. 4 in section, a damping foil, laid on a sheet to be damped,in accordance with a further exemplary embodiment,

[0016]FIG. 5 the temperature dependence of the loss factor, determinedin accordance with a bending vibration test, of an exemplary embodimentof damping foil in accordance with FIG. 2.

[0017]FIG. 1 shows in perspective and in exploded illustration a dampingfoil 2 viewed towards the side 13, facing the part to be damped, of a“lower” layer 3, facing the part to be damped, of the damping foil 2.The damping foil 2 further has “upper” layer 4, facing away from thepart to be damped, and a film-like intermediate layer 5, formed by meansof non-woven fabric or by means of kraft paper, between the layers 3 and4 of the damping foil 2. On the side 13 facing the part to be dampedthere may be applied an adhesive such as a hot-melt glue 12 or adispersion glue. The lower layer 3 of the damping foil 2 is formed, atleast in the region of this side 13, as an element attaining at least atemporary adherent connection with the part to be damped. In accordancewith a first exemplary embodiment there are embedded in the material ofthe lower layer 3 magnetised or magnetisable particles (for examplefollowing DIN 17470 and DIN 50470), in the following briefly referred toas ferrite powder.

[0018] For weight reduction this lower layer 3 has openings 7, of whicha few are Illustrated. These openings are expediently formed for simpleproduction in the manner of perforations penetrating through the entirelower layer 3. Further, impressions 11 are advantageously provided inthe side 13 of the lower layer 3, which are so arranged that theyconnect the openings 7. They serve, in the heat treatment for activatingthe hot-melt glue 12, to prevent that air inclusions remain between thepart to be damped and the side 13 of the layer 3. The surface pattern ofthe impressions 11 is thereby not restricted to the pattern illustratedin FIG. 1. A significant factor is that the impressions 11 are providedfor each of the openings 7,

[0019] The void proportion of the openings 7 amounts expediently toabout 5 to 30% of the lower layer 3. Expediently, the lower layer 3 hasa thickness of from 0.2 to 1.2 mm, preferably from 0.5 to 1 mm and is ofa bitumen or a bitumen mixture with a ferrite powder component amountingto about 50 to 70 weight percent. The upper layer 4 of the damping foil,containing no such magnetic or magnetisable particles, and away from thepart to be damped, is about 0.8 to 2 mm thick and is expedientlylikewise of bitumen or a bitumen mixture. This upper layer 4 is fixedlybonded with the lower layer 3 having the openings 7, for example bymeans of gluing or lamination. For reasons of acoustics it is ofsignificant advantage to provide between these two layers 3 and 4 a thinintermediate layer 5 of nonwoven fabric or kraft paper. The thickness ofthis intermediate layer 5 is of the order of 0.1 mm. It may be laminatedor glued onto the lower layer 3, onto which in turn the upper layer 4 islaminated or glued. Of advantage is an intermediate layer 5 constitutedto be adhesive on both sides. As explained below with reference to FIG.2 and FIG. 4, the intermediate layer 5 may be continuous (FIG. 2) or maylikewise have openings 8 (FIG. 4).

[0020] The side 14 of the upper layer 4 of the damping foil 2 away fromthe part to be damped is the so-called “sight side”, which in manyapplications, in particular in the damping of body panels, is paintedover. It may thus expediently have a further cover layer 6 (FIG. 2 andFIG. 3), which stabilises the long-term behaviour of this sight side 14.The cover layer 6 can be formed by a per se known antiblocking coating,for avoiding blocking during transportation or storage, or can also beformed by a dispersion coating in order to reduce the externally visibleeffect oyellowing in the case of light coloured paints. This cover layer6 is, however, not necessary if there is no reason to fear a risk ofblocking or a risk of yellowing.

[0021]FIG. 2 shows the application of the damping foil 2 onto a part tobe damped, in particular a sheet 1. With the exemplary embodiment inaccordance with FIG. 2 there is provided an intermediate layer 5 whichis not perforated. By these means it is prevented that material of theupper layer 4 can enter into the openings 7, which could arise under theeffect of heat, this sinking then possibly being visible in the sightside 14 directed outwardly. This exemplary embodiment is then ofparticular advantage if the two layers 3 and 4 are to be produced as webor sheet material and then laminated onto one another.

[0022] Another manner of production is however conceivable, namely thatwith the layer 3, produced as web or sheet material with openings 7provided therein, the material forming the layer 4 is directly appliedsuch that it can penetrate complete or partly into the openings 7, whichis illustrated by means of the stopple-like penetrations 9. By thesemeans an extremely good, firm connection between the two layers 3 and 4is ensured. This is illustrated in more detail in FIG. 3. In order to beable, to attain the generally desired high loss factor, here also it isexpedient to provide an intermediate layer 5. In order likewise to beable to attain penetrations, it is expedient also to provide theintermediate layer 5 with corresponding openings 8, which align with theopenings 7 in the lower layer 3. It is however in no sense urgentlyrequired that all openings 7 in the lower layer 3 align with therespective associated openings 8 in the intermediate layer 5. This isnecessary merely to the extent that firm connection between lower layer3 and upper layer 4 is ensured. Thereby it is to be taken intoconsideration that the penetrations 9 have higher weight than the airinclusions in the openings 7 in the embodiment according to FIG. 2.

[0023] In FIG. 2 the ferrite powder particles which bring about themagnetic or magnetisable properties of the upper damping foil 2 arerepresented by points 10. By ferrite powder particles there should bemerely understood inclusions which can attain the desired effect, namelythe adhering of the damping foil 2 to the sheet 1 to be damped, at leastduring the heat treatment after the application of the damping foil 2onto the sheet 1 for the attainment of the firm connection by means of ahot-melt glue, as is explained above. This adhesion can be effected bymeans of the magnetic properties of these particles 10 themselves, or bymeans of the capability to cooperate with permanent magnets provided onthe other side of the sheet 1.

[0024] This (as a rule only temporary) adhesion can however also bebrought about completely or in part by means of per se known so-calledadhesive constituting of the lower layer 3. This adhesive constituting,which permits an adherent wide area connection of the damping foil 2with the sheet 1, whereby however the damping foil 2 can be againremoved completely intact, is in particular attained in that the layeron the side 13 towards the sheet 1, or in the section neighbouringthereto, has a layer structure of a strongly deficiently cross-linkedpolyurethane. With bitumen, in particular blown bitumen, this isattainable by means of the mixing of an atactic propylene in aproportion of atactic polypropylene to bitumen of about 1:3. In themixing of the material for the lower layer 3 the viscosity in the meltat 180° C. is advantageously about 50,000 mPa.s and more, with apenetration value in accordance with DIN1995 between 15 and 55,preferably 35 and 55.

[0025] To make more clear the sound-damping function of the damping foil2, FIG. 5 shows the result of a bending vibration test, measured inaccordance with DIN 53440 at a frequency of 200 Hz.

[0026] In accordance with the invention it is also possible that thelower layer 3 is both constituted to be adhesive and also provided withferrite particles.

[0027] With regard to the weight saving that can be achieved it shouldbe noted that conventional single-layer or double-layer damping foils,which attain a loss factor of more than 0.1 at 0° C. to 35 . . . 40° C.,have a weight per unit area which is 5 kg/m² and more. With applicationof the present inventions these weights per unit area overall can bereduced significantly, to about 4.2 kg/m² and less.

1. Multi-layer damping foil (2) the lower layer (3) of which, facing thepart (1) to be damped, has properties which are suitable for theadhering of the damping foil (2) onto the part (1), and the upper layer(4) thereof, facing away from the part (1), does not have the adherenceproperties, characterised in that, the lower layer (3) has numerousthrough-openings (7).
 2. Damping foil according to claim 1,characterised in that, the lower layer (3) has, on the side (13) facingthe part (1), impressions (11) which connect to the openings (7) withone another.
 3. Damping foil according to claim 1 or 2, characterised inthat, there is provided between lower and upper layer (3, 4) a thin,film-like intermediate layer (5).
 4. Damping foil according to claim 3,characterised in that, the intermediate layer (5) has openings (8) whichalign with the openings (7) in the lower layer (3).
 5. Damping foilaccording to claim 3 or 4, characterised in that, the intermediate layer(5) is a non-woven fabric or kraft paper layer.
 6. Damping foilaccording to any of claims 3 to 5, characterised in that, theintermediate layer (5) is provided on both sides with a glue layer, forconnection with the lower and upper layers (3, 4).
 7. Damping foilaccording to any of claims 1 to 6, characterised by an openingproportion (void proportion) of 5 to 30 percent.
 8. Damping foilaccording to any of claims 1 to 6, characterised in that, the lowerlayer (3) contains magnetic or magnetisable particles (10).
 9. Dampingfoil according to claim 8, characterized in that, the particles (10) arepresent in a proportion of 50 to 70 weight percent.
 10. Damping foilaccording to any of claims 1 to 9, characterised in that, on its side(13) facing the part (1), the lower layer (3) has a dispersion gluelayer or a hot-melt glue layer (12).
 11. Damping foil according to anyof claims 1 to 10, characterised in that, on its side (14) facing awayfrom the part (1), the upper layer (4) has a dispersion coating, anantiblocking coating or similar surface covering layer (6).
 12. Dampingfoil according to any of claims 1 to 11, characterised in that, the basematerial of upper (4) and/or lower (3) layer is a bituminous material.13. Damping foil according to any of claims 1 to 12, characterised inthat, the lower layer (3) has a thickness of about 0.3 to 1.2 mm, theupper layer (4) has a thickness of about 0.8 to 2 mm, and if applicablethe intermediate layer has a thickness of about 0.1 mm.
 14. Damping foilaccording to any of claims 1 to 13, characterised in that, the dampingfoil (2) is so dimensioned that the loss factor is more than 0.1 at 0 to35 . . . 40° C., the mass per unit area being less than 5 kg/m²,preferably less than 4.2 kg/m².
 15. Damping foil according to any ofclaims 1 to 14, characterised in that, for provision as an adhesive,intact removable damping foil (2), but nonetheless to bring about anadherent connection with the part (1), the lower layer (3), at least itssection facing the part (1), has a layer structure of a stronglydeficiently cross-linked polyurethane.
 16. Damping foil according toclaim 15, characterised in that, the lower layer (3) is a mixture ofbitumen, in particular blown bitumen and atactic polypropylene (APP).17. Damping foil according to claim 15, characterised by a ratio ofatactic polypropylene to bitumen of about 1:3.
 18. Damping foilaccording to claim 16 or 17, characterised by a viscosity in the melt at180° C. of >=50000 mpa.s and a penetration value according to DIN 1995between 15 and 55, preferably between 35 and
 55. 19. Method for theproduction of multi-layer damping foil (2) in accordance with anypreceding claim, having the steps production of a layer (3) which issuitable for adhering on a part to be damped (1), perforating the layer(3) and applying, in particular laminating, a further, upper layer (4)onto the first-mentioned lower layer (3).
 20. Method according to claim19, characterised in that, before or after the perforation, there isapplied, in particular laminated, onto the first-mentioned, lower Layer(3), a thin, flexible intermediate layer (5).
 21. Method according toclaim 19 or 20, characterised by embossing of depressions into thefirst-mentioned, lower layer (3) on the side (13) thereof away from theupper layer (4) after the application thereof, such that thesedepressions connect with one another the openings (7) formed by means ofthe perforation.